The present invention relates generally to optical communications, and specifically to a fused fiber interleaver/deinterleaver.
Optical transmission systems, including optical fiber communication systems, have become an attractive alternative for carrying voice and data at high speeds. In addition to the pressure to improve the performance of optical communication systems, there is also increasing pressure on each segment of the optical communication industry to reduce costs associated with building and maintaining an optical network.
One technology used in optical communication systems is wavelength division multiplexing (WDM). As is well known, WDM pertains to the transmission of multiple signals (in this case optical signals) at different wavelengths down a single waveguide, providing high-channel capacity. Typically, the optical waveguide is an optical fiber.
For purposes of illustration, according to one International Telecommunications Union (ITU) grid a wavelength band from 1530 nm to 1565 nm is divided up into a plurality of wavelength channels, each of which have a prescribed center wavelength and a prescribed channel bandwidth. The spacing between the channels is also prescribed by the ITU grid, and is in units of frequency or wavelength.
For example, one ITU channel grid has a channel spacing requirement of 100 GHz (in this case the channel spacing is referred to as frequency spacing), which corresponds to channel center wavelength spacing of 0.8 nm. With 100 GHz channels spacing, channel xe2x80x9cnxe2x80x9d would have a center frequency 100 GHz less than channel xe2x80x9cn+1xe2x80x9d (or channel n would have a center wavelength 0.8 nm greater than channel n+1). The chosen channel spacing may result in 40, 80, 100, or more wavelength channels across a particular passband. While transmission of information via an optical medium has afforded significant improvements in the transmission of voice and data, the increased demand for capacity may still adversely impact signal quality of the transmitted optical signal. For example, the number of channels that may be carried in a signal optical fiber is limited by cross talk, narrow operational bandwidth of amplifiers, and optical waveguide non-linearities. The more the information that is sent over a particular transmission medium, the greater the number of channels that are needed. It follows, that due to bandwidth considerations, the larger the number of channels, the closer the separation between adjacent channels must be. In an attempt to address the need for increased channel density in WDM
Not only is it difficult to interleave signals with ever-decreasing channel spacing, but also it is difficult to deinterleave the channels at the receive-end. To this end, in order to preserve the integrity of the signal at the receiver end of the communication link, cross talk in the form of received channel overlap must be minimized. As can be appreciated, the closer the channel spacing is, the more difficult it is to prevent inter-channel interference.
What is needed, therefore, is an interleaver/deinterleaver apparatus and corresponding method of its use, which addresses the needs of the optical communications industry, while overcoming at least the shortcomings of the conventional approaches described above.
In accordance with an exemplary embodiment of the present invention, an optical interleaver/deinterleaver includes a substrate having at least one window therein. The interleaver/deinterleaver further includes a first optical waveguide and a second optical fiber, which are disposed over a substrate. The first and second optical waveguides are coupled together at at least two locations forming optical couplers at each of the locations. The first optical waveguide has a first length between the two locations, and the second optical waveguide has a second length between the two locations wherein the first length is smaller than the second length. Illustratively, the first optical waveguide is disposed over the window, so that the window is along the first length of the first optical fiber.
In accordance with another exemplary embodiment of the present invention, a method of interleaving/deinterleaving optical signals includes providing a first optical waveguide and a second optical waveguide, which is coupled to the first optical fiber at at least two locations. The method further includes adjusting a length of the second optical waveguide to coarsely adjust channel separation, and applying laser energy to the first optical waveguide to finely adjust the channel separation.